The present invention relates to a ball screw. Such ball screws convert a rotating motion into a linear motion.
From U.S. Pat. No. 6,176,149 and DE 100 44 447 A1, for example, a ball screw has become known, with a ball roller screw and a screw nut arranged thereon. Balls are arranged so that they can circulate endlessly in an endless ball channel limited by helical, spiral ball tracks of the ball roller screw and the screw nut. The ball channel comprises a load section wound about the ball roller screw, whose beginning and end are endlessly connected to each other by a load-free return section. In the ball screw disclosed by U.S. Pat. No. 6,176,149, a plurality of spacers having concave surfaces are arranged between adjoining balls to reduce friction between adjoining balls. However, in this configuration, the individual spacers do not restrict the balls' movement along the ball channel and ball clogging can still occur. In the ball screw disclosed by DE 100 44 447 A1, two balls are housed in a common ball cage, whose cage pockets each house one of the balls. The ball cage is formed of a flat, disc-shaped base with oval outer contours, in which two circular recesses form the pockets for the balls. The pocket walls are slightly concave and enclose a portion of the ball circumference on both sides of an equatorial plane, so that the balls are held in these pockets so that they cannot be lost. Due to the minimal wrap-around by means of the concave pocket walls, a pronounced dip by the balls in these cage pockets is set. This dip—or also pocket play—could be reduced in that the ball cage and thus the ball wrap-around have a thicker configuration. However, thicker ball cages are associated with other disadvantages: the ball cage extends along the ball channel. In this extension direction, the ball cage has webs, which are arranged parallel to the ball tracks but outside of these ball tracks. The radial spacing between the outer periphery of the ball roller screw and the inner periphery of the screw nut must be constructed at least as large as the thickness of this web, so that the ball screw is functional. If the ball cage has a thicker construction, that is, if the web is also thicker, then this leads to the result that this radial spacing increases. The ball screw then has a larger structure. Another problem presents itself in the region of the return section. In the return section, typically there is a groove, in which this web runs. If this web now has a thicker construction, then the groove and thus the return section must have a larger construction.